why were the slaves that manned captain Auld's cessel esteemed so highly?

The were esteemed and held high by the other slaves because manning the Captain's vessel was considered a great privilege and it was a great opportunity to see other places and things.

"My master's son-in-law, Captain Auld, was master of the vessel; she was otherwise manned by the colonel's own slaves. Their names were Peter, Isaac, Rich, and Jake. These were esteemed very highly by the other slaves, and looked upon as the privileged ones of the plantation; for it was no small affair, in the eyes of the slaves, to be allowed to see Baltimore."